Chemiluminesceht process

ABSTRACT

1. A PROCESS FOR DETERMINING THE CONCENTRATION OF A GASEOUS CONSTITUENT IN A GASEOUS SAMPLE MIXTURE BY MEASURING THE (CHEMILUMINESCENT) CHEMILUMINESCENCE OF A   REACTION BETWEEN THE CONSTITUENT AND A GASEOUS REACTANT IN A REACTION CHAMBER COMPRISING INTRODUCING THE GASEOUS SAMPLE MIXTURE INTO THE REACTION CHAMBER WITH SUBSTANTIALLY LAMINAR FLOW AT A LOCATION PROXIMATE TO LIGHT TRANSMITTING MEANS FORMING AT LEAST A PORTION OF A WALL OF THE REACTION CHAMBER, SEPARATELY INTRODUCING A GASEOUS REACTANT CAPABLE OF PRODUCING CHEMILUMINESCENCE WHEN REACTING WITH THE CONSTITUENT INTO THE REACTION CHAMBER AT A LOCATION PROXIMATE TO THE POINT OF INTRODUCTION OF THE GASEOUS SAMPLE MIXTURE, DRAWING THE GASEOUS MIXTURE OF SAMPLE AND REACTANT AWAY FROM THE LOCATION AT WHICH IT IS INTRODUCED INTO THE REACTION CHAMBER, AND MEASURING THE CHEMILUMINESCENCE TRANSMITTED THROUGH THE LIGHT TRANSMITTING MEANS THAT IS PRODUCED BY THE REACTION BETWEEN THE CONSTITUENT AND THE REACTANT.

March 25, 1975 A. WARNICK Er CHEIILUIINESCBNT PROCESS Origin Filed lay26, 1971 3Z .EREADOUT| 2 Shuts-Sheet 1 FlG.l ELECTRONIC AMPLll-IER FLOWFLOW METERING METERING SAMPLE I A. REACTANT MIXTURE /Z M 24 MIXTURE lNVENTORS AZA/V WQ/G/V/CK Ali) 0. COlI/N ATTORNEYS Much 25, 1975 A.WARNICK ETAL Rs. 28,376

CHEIILUIIHESCEHT PROCESS Original Filed lay 26, 1971 2 Shuts-Sheet a512i F G. 5

I i f 22a v I 5 HF? m lNVENTORS AlA/V WflB/V/CK Alix a COZV/A/ ATTORNEYSUnited States Patent Re. 28,376 Reissuecl Mar. 25, 1975 28,376CHEMILUMINESCENT PROCESS Alan Warnick and Alex D. Colvin, Oak Park,Mich., assignors to Ford Motor Company, Dearbom, Mich. Original No.3,746,513, dated July 17, 1973, Ser. No. 146,929, May 26, 1971.Application for reissue Dec. 17, 1973, Ser. No. 425,643

Int. Cl. G01n 27/68 U.S. Cl. 23-232 R 16 Claims Matter enclosed in heavybrackets If] appears in the original patent but forms no part of thisreissue specification; matter printed in italics indicates the additionsmade by reissue.

ABSTRACT OF THE DISCLOSURE Concentrations of nitric oxide in gaseousmixtures are determined by measuring the chemiluminescence of thereaction between the nitric oxide and ozone. The gaseous mixture isintroduced with virtually laminar flow into a reaction chamber at alocation proximate to the inner surface of a light transmitting element.Reaction chamber pressure preferably is maintained above about 5 torr.

BACKGROUND OF THE INVENTION This invention relates to that ofconcurrently filed U.S. patent application Colvin et al. Ser. No.146,927.

Recent interest in reducing the quantity or proportion of harmfulconstituents in the atmosphere has provided considerable impetus to thedevelopment of processes and devices for reducing the amounts of suchconstituents in exhaust gases from vehicle engines, furnaces, and otherpower generating equipment. Such development has been hindered becausean instrument capable of accurately, etficiently and economicallymeasuring very small quantities of constituents in gaseous mixtures hasnot been available.

The chemiluminescence of certain reactions has been known for some timeand recent investigations have produced instruments capable of utilizingchemiluminescence as an analytical tool. One of such instruments usesthe chemiluminescence of the reaction between nitric oxide and ozone todetermine the concentration of nitric oxide or ozone in gaseous mixturesby blending the gaseous mixture with a known quantity of the otherreactant in a well-stirred reactor at extremely low pressures of onetorr or less. A photosensitive device measures the intensity of theresulting chemiluminescence and applies an output signal to a calibratedmeter.

Considerable difficulties have been encountered in attempting to utilizethat instrument and its technique on a broad basis. structurally, alarge vacuum pump is necessary to produce the extremely low pressures inthe reaction chamber and such pumps increase instrument costs to anuneconomical level. The extremely low pressures also accentuate sealingdifficulties and necessitate precision manufacturing and assemblyprocedures. Operationally, transient conditions tend to occur during thewell-stirred mixing of the gaseous mixture and the reactant and thesetransient conditions interfere significantly with reproducibility.sensitivity, and overall accuracy.

SUMMARY OF THE INVENTION This invention provides a sensitive, accurate,versatile and economical instrument and process for measuring thechemiluminescence of a reaction between a constituent of a gaseousmixture and a gaseous reactant to determine the concentration of theconstituent. The invention is useful particularly in measuring theconcentration of nitric oxide in a gaseous mixture. Nitric oxideconcentrations ranging from a few parts per billion tbru several partsper hundred can be measured accurately and efficiently with theinvention. Higher pressures are utilized in the invention to improvereproducibility and economic aspects of the instrument. Sensitivity andaccuracy are maximized by ignoring the well-stirred reactor techniquesof the prior art and emphasizing instead a technique that maintains asubstantially stable portion of the reaction as close as possible to alight sensing device.

An instrument for carrying out the invention comprises a reactionchamber having an opening at one end with a light transmitting elementsealingly mounted in the opening. A sample conduit for supplying thegaseous mixture to the reaction chamber opens into the reaction chamberat a location proximate to the inner surface of the light transmittingelement. A reactant conduit supplies to the reaction chamber a gaseousreactant capable of reacting with a constituent of the sample mixture ina manner that produces chemiluminescence An exhaust conduit removes thereaction products from the reaction chamber. A light sensing device suchas a photomultplier tube is connected to the reaction cham her where itreceives the light passing through the light transmitting elementproduces accurate, continuous readtaking place within the chamber.

The invention is highly suited to measuring the concentration of nitricoxide in a gaseous sample mixture by reacting the nitric oxide withozone. Such sample mixture enters the reaction chamber through thesample conduit and a gaseous reactant mixture containing at least apredetermined minimum amount of ozone enters the reaction chamberthrough the reaction conduit. Reaction begins immediately and a portionof the reaction that depends on the concentration of the nitric oxide inthe sample mixture occurs within a short distance of the lighttransmitting element. Continuously flowing the gaseous mixtures into thereaction chamber and measuring the chemiluminescence transmitted throughthe light transmitting element produces accurate, continuous readoutsover a wide range of nitric oxide concentrations.

Pressure in the reaction chamber must be sufficiently high to avoidexcess turbulence and to promote uniform reaction proximate to the lightsensing device. Best resuits are achieved when the absolute pressure inthe reaction chamber is maintained above about 5 torr with preferredpressure ranging above 300 torr, because the gases then enter and flowthrough the reaction chamber with virtually laminar flow. The smooth.stable reaction reduces transient mixing variations and the resultingvariations in the light reaching the light sensing device. Such higherpressures also increase the reaction rate and thereby maintain a greaterportion of the reaction proximate to the light sensing device. Theresulting increase in light intensity further improves accuracy andsensitivity. Reaction chamber pressures approximating atmosphericpressure can be used if desired;

An exhaust pump can be connected to an exhaust outlet of the reactionchamber to draw the sample mixture and the reactant mixture through thereaction chamber. Metering devices then are included in the sample conduit and the reactant conduit; such metering devices typically are finecapillary tubes that are located a sufficient distance upstream of thereaction chamber to permit dissipation of any turbulence producedthereby. If operation above atmospheric pressure is desired, pumps areincluded in the sample conduit and the reactant conduit and the exhaustoutlet is connected to the atmosphere through an appropriate meteringdevice.

Optimized fiow rates of the sample mixture and the reactant mixturedepend on the quantity and nature of the other constituents in thegaseous mixtures, assuming of course that the proportions of thereactants are within a predetermined range. Carbon dioxide for examplehas a quenching efl'ect on the emitted chemiluminescence of the nitricoxde and ozone reaction approximately 2-3 times that of oxygen, whichusually forms the greater portion of the ozone containing reactantmixture. The quenching effect is minimized in sample mixtures containinga high proportion of carbon dioxide by providing relatively high how ofthe reactant mixture to insure a high ratio of oxygen to carbon dioxidein the reaction chamber. Thus, best results are achieved when analyzingautomotive exhaust gases (which contain a high proportion of carbondioxide) by providing about 4 volumes of reactant mixture for eachvolume of sample mixture, while analyzing atmospheric sample mixturespreferably is conducted with about 4 volumes of sample mixture for eachvolume of reactant mixture. Analysis of most other mixtures can beperformed within these ratios.

For the nitric oxide-ozone reactions, the light trans mitting elementand the light sensing device preferably transmit and measure light in abroad portion of the spectrum including wavelengths between about 6400Angstroms and 25,000 Angstroms. Improved results can be achieved bymeasuring light having wavelengths of about 6400-l5,000 Angstrorns only.Spurious noise is minimized further by measuring light havingwavelengths of about 10,000-l4,000 Angstroms only.

A cylindrical housing serves preferably as the reaction chamber. Adisc-shaped light transmitting element is mounted sealingly in one endof the cylindrical housing and the other end is closed except for theexhaust outlet. The sample conduit extends through the cylindrical wallof the housing and opens into the reaction chamber at a locationproximate to the light transmitting element. Reactant preferably isintroduced into the reaction chamber from a reactant conduit openingadjacent the sample conduit opening or between the sample conduitopening and the exhaust outlet.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustrating thebasic structural and operational principles of the invention. FIG. 2 isa partially sectioned view through a reaction chamber for the instrumentin which smoothly curved conduits introduce both the sample mixture andthe reactant into the reaction chamber at a location proximate to thecentral portion of a light transmitting element. FIG. 3 is an elevationof the reaction chamber shown in FIG. 2. FIG. 4 is a cross section of analternate reaction chamber design in which a smoothly curved conduitintroduces the sample mixture at a location proximate to the centralportion of the light transmitting element and a straight conduitintroduces the reactant into the reaction chamber at a location betweenthe sample mixture outlet and the exhaust conduit. FIG. 5 is a crosssection of a reaction chamber in which a straight conduit introduces thesample mixture into the reaction chamber at a location closely adjacentan edge of the light transmitting element and another straight conduitintroduces the reactant at a location diametrically across from themixture outlet and axially removed therefrom toward the exhaust conduit.The reaction chamber of FIG. 6 is a similar to that of FIG. 5 exceptthat the reactant enters the chamber on the same side as the samplemixture. FIG. 7 shows another reaction chamber in which the reactantenters the reaction chamber through an annular conduit that surroundsthe sample conduit.

DETAILED DESCRIPTION Referring to FIGS. 1-3, a gaseous sample mixturecontaining an unknown quantity of nitric oxide is conducted by conduit10 to a capillary type flow metering device 12. A sample conduit 14introduces the sample mixture leaving the flow metering device into acylindrical reaction chamber 16. A conduit 18 conduits a gaseousreactant mixture containing at least a predetermined minimum amount ofozone to a capillary type flow metering device 20 and a reactant conduit22 introduces the reactant leaving the flow metering device intoreaction chamber 16. One end of reaction chamber 16 has an outletfitting 24 attached thereto and a vacuum pump 26 is connected to fitting24. A photomultiplier device 28 is mounted on the other end of reactionchamber 16 and is connected electrically through an amplifier 30 andother appropriate electronic circuitry to a readout device 32.

Outlet fitting 24 communicates with the interior of reaction chamber 16through an opening 34 in an end wall thereof (FIG. 2). A disc-shapedlight transmitting element 38 closes the entire opposite end 35 of thechamber so that outlet fitting 24 is axially removed from element 38.The housing of photomultipleir device 28 is threaded into the reactionchamber to maintain element 38 in place. Appropriate seals 40 and 42assure gas tight installation of element 38 in opening 35. A flange 44provides for fastening the assembly of reaction chamber 16 andphotomultiplier device 28 to supporting structure (not shown).

Sample conduit 14 extends through the cylindrical wall of chamber 16approximately at its longitudinal midpoint and curves smoothly towardlight transmitting element 38 so the opening 46 at the end of the sampleconduit is proximate to the inner surface of element 38. Reactantconduit 22 extends through the cylindrical wall of re action chamber 16at a location diametrically opposed to conduit 14 and conduit 22 alsocurves smoothly toward light transmitting element 38 so the opening 48at its end also is proximate to the inner surface of element 38. Opening48 is in the same plane as opening 46 and is adjacent to opening 46.Both openings 46 and 48 are located in the central portion of reactionchamber 16 and both are located axially between light transmittingelement 38 and exhaust opening 34.

Reaction chamber 16 typically is about 2 inches in diameter and about 3inches long. Conduits 14 and 22 have an inside diameter of about /a inchand a wall thickness of about inch. Element 38 is a glass optical filtercapable of transmitting light in at least the dark red portion of thevisible region and the infrared region (above about 6400 Angstromunits). Openings 46 and 48 are about A inch from the inner surface ofelement 38 and are spaced apart about l 4 inch.

Instrument operation occurs in the following manner. Pump 26 is startedand capillary metering devices 12 and 20 are selected so thesubatmospheric pressure within reaction chamber 16 reaches somepredetermined value. Good results are achieved when the predeterminedvalue of pressure is at least about 5 torr. A reactant mixturecontaining about 2 percent ozone and 98 percent oxygen is supplied toreactant conduit 18. As sample mixture flows into reaction chamber 16through opening 46, nitric oxide molecules in the sample mixture reactwith ozone molecules in the reactant mixture to producechemiluminescence in an amount proportional to the concen tration of thenitric oxide in the gaseous mixture.

Both the sample mixture and the reactant mixture flow into the reactionchamber with substantially laminar fiow. In the reaction chamber, themixtures blend with each other and pass through the reaction chamberwith a minimum of turbulence. This stability provides a high degree ofreproducibility and sensitivity.

Light from the chemiluminescence passes through element 38 and itsintensity is detected by photomultiplier device 28. An electronic signalrepresenting the intensity is transmitted to electronic amplifier 30which in turn applies an output signal to readout device 32 that iscalibrated to read directly in units representing the conconcentrationof nitric oxide in the gaseous mixture.

Accuracy and sensitivity are maximized when a con siderable portion ofthe reaction between the nitric oxide and the ozone occurs proximatelyto the inner surface of element 38. Sample conduit 46 in fact directsthe sample mixture toward the light transmitting element as the mix tureenters the reaction chamber. The reaction continues.

as the reacting compositions move through reaction chamber 16 towardexhaust opening 36 but the intensity of the light received by lightsensing device 28 diminishes with the decreasing solid angle subtendedby light transmitting element 38.

Increased reaction rates can be achieved by raising the pressure in thereaction chamber since the higher pressure increases the number ofmolecules of nitric oxide and ozone in the chamber and thereby increasesthe probability of molecule collision. Highly accurate results withexcellent sensitivity are achieved by raising the reaction chamberpressure to at least about 300 torr. Such higher pressures permit thegaseous mixture and the reactant to enter the reaction chamber with animproved laminar type flow that diminishes transient variations in thelight intensity resulting from nonuniform mixing within the reactionchamber.

In the reaction chamber of FIG. 4, sample conduit 14a is similar to thatof FIG. 2 but a straight reactant conduit 22a terminates a shortdistance just inside the cylindrical wall of the reaction chamber sothat its opening 48a is directed radially inward in a plane locatedaxially between the sample conduit opening and the exhaust conduitopening. Conduit 22a preferably enters the chamber within about one halfof the axial length of the chamber from light transmitting element 38.Comparative tests with a FIG. 4 reaction chamber 3 inches long andhaving conduit 22a 1.5 inches from element 38 indicate slight increasesin measurable light intensity over the FlG. 2 chamber.

In the reaction chamber of FIG. 5, the location of reactant conduit 22bis similar to that of FIG. 4. Sample conduit 14b is straight and extendsradially into the cham her at a location closely adjacent an edge oflight transmitting element 38. Openings 48b of the reactant conduit isdiametrically across and axially displaced toward the exhaust openingfrom the opening of the sample conduit. In comparative tests with theFIG. 2 reaction chamber, the FIG. 5 arrangement also produced slightincreases in measurable light intensity.

Both conduits enter the reaction chambers of FIGS. 6 and 7 on the sameside. In FIG. 6, the location of sample conduit 140 is similar to thatof FIG. 5 while reactant conduit 22c is displaced axially therefromtoward the exhaust opening. In FIG. 7, sample conduit 14d extendsstraight into the reaction chamber and reactant conduit 22d surroundsthe sample conduit so the reactant conduit forms an annular opening 48d.

In each of these reaction chambers, the sample conduit is proximate tothe light sensing assembly to promote reaction proximate thereto. Eachof the disclosed reaction chamber constructions and similarconstructions produce useful results although the best combination ofaccuracy and sensitivity has been achieved to date with the chambers ofFIGS. 2, 4 and 5.

Flow metering devices 12 and preferably are at least several inchesupstream from the respective conduit openings to permit dissipation ofany turbulence produced thereby. The use of capillary tubes as themetering devices provides stable metering and minimal turbulence.Appropriate converters can be included in the sample conduit to convertother oxides of nitrogen into nitric oxide and thereby permit using theinvention to provide the total concentration of oxides of nitrogen inthe sample mixture. An ozone killer can be included between the reactionchamber and the pump to increase the life of rubber seals and otherrubber pump components. Other light sensing devices capable ofresponding to light having the aforementioned wavelengths can besubstituted for the photomultiplier device.

Thus this invention provides improved structures and techniques foraccurately and conveniently determining the concentrations of gases suchas nitric oxide in a gaseous mixture. The invention has greatly improvedsensitivity, reproducibility, and economy of construction and operation.

1. A process for determining the concentration of a gaseous constituentin a gaseous sample mixture by meas uring the [chemiluminescent]chemiluminescence of a reaction between the constituent and a gaseousreactant in a reaction chamber comprising introducing the gaseous samplemixture into the reac tion chamber with substantially laminar how at alocation proximate to light transmitting means forming at least aportion of a wall of the reaction cham ber,

separately introducing a gaseous reactant capable of producingchemiluminescence when reacting with the constituent into the reactionchamber a! a location proximate to the point of introduction of thegaseous sample mixure,

drawing the gaseous mixture of sample and reactant away from thelocation at which it is introduced into the reaction chamber, and

measuring the chemiluminescence transmitted through the lighttransmitting means that is produced by the reaction between theconstituent and the reactant.

2. The process of claim 1 in which the reactant is included in a gaseousreactant mixture that is introduced into the reaction chamber withsubstantially laminar flow 3. The process of claim 2 in which thegaseous mixtures blend smoothly with each other within the reactionchamber as the mixtures are drawn substantially perpendicularly awayfrom the light transmitting means.

4. The process of claim 3 in which the sample mixture is introduced intothe reaction chamber at a location closely adjacent the lighttransmitting means.

5. The process of claim 4 in which the reactant mixture is introducedinto the reaction chamber at a location positioned across at least aportion of the light transmitting means from the location at which thesample mixture 15 introduced.

6. The process of claim 5 comprising maintaining the pressure in thereaction chamber above about 5 torr.

7. The process of claim 6 comprising maintaining the pressure in thereaction chamber above about 300 torr.

8. The process of claim 7 in which the gaseous mixture is introducedinto the reaction chamber at the central portion of the lighttransmitting means, said gaseous mixture being directed toward the lighttransmitting means at its introduction into the reaction chamber.

9. The process of claim 7 in which the sample mixture is introduced intothe reaction chamber at one side of the light transmitting means, saidsample mixture flowing substantially parallel to the light transmittingmeans at its introduction into the reaction chamber.

10. The process of claim 9 comprising maintaining the relative flowrates of the sample mixture and the reactant mixture within a range ofabout 4:1 to 1:4.

11. The process of claim 1 comprising maintaining the pressure in thereaction chamber above about 5 torr.

12. The process of claim 1 comprising maintaining the pressure in thereaction chamber above about 300 torr.

13. The process of claim 1 in which the gaseous mixture is introducedinto the reaction chamber at the central portion of the lighttransmitting means, said gaseous mixture being directed toward the lighttransmitting means at its introduction into the reaction chamber.

14. The process of claim 1 in which the sample mixture is introducedinto the reaction chamber at one side of the light transmitting means.said sample mixture flowing substantially parallel to the lighttransmitting means at its introduction into the reaction chamber.

15. The process of claim 1 comprising maintaining the relative flowrates of the sample mixture and the reactant mixture within a range ofabout 4:1 to 1:4.

References Cited The following references, cited by the Examiner. are 01record in the patented file of this patent or the original patent.

UNITED STATES PATENTS $345,758 4/1966 Benzinger et al. 23-230 3.285.7031171966 Narita et al. 23-354 3,287,089 11/1966 Wilburn 23-254 83,520,660 7/1970 Webb 23-253 3,615,241 10/1971 Low 23253 3,647,3873/1972 Benson ct a1. 23-254 OTHER REFERENCES Warren et al.: PortableEthylene Chemiluminescence Ozone Monitor, Rev. Scient. Instr., vol. 41,pp. 280-282 R. E. SERWIN, Primary Examiner 23230 PC, 232 E

1. A PROCESS FOR DETERMINING THE CONCENTRATION OF A GASEOUS CONSTITUENTIN A GASEOUS SAMPLE MIXTURE BY MEASURING THE (CHEMILUMINESCENT)CHEMILUMINESCENCE OF A